Preheat the oven to 425°F Arrange the lemon slices in a single layer down the center of a roasting pan. Rub the chicken with the oil and season with salt and pepper. Place the chicken skin side up on the lemon slices and bake for 35 minutes. Transfer to the boiler and cook until the skin is crisp, about 3 minutes. Drizzle the chicken with the lemon juice.
Meanwhile, using a food processor, mix together the peas, ricotta, 1/2 teaspoon tarragon and 1/4 teaspoon salt.
On a work surface, working with 2 wonton wrappers at a time, spoon a teaspoon of the pea mixture onto the center of each wrapper. Moisten the edges with water and fold the wrapper in half diagonally to form a triangle, pushing out any air pockets and pressng the edges firmly to seal. With the long side of the triangle facing you, fold the top point back toward you, then fold the right and left points to meet and press all 3 points firmly together, sercuring with more water.
In a large pot of boiling, salted water, cook the tortellini until they float to the top, about 5 minutes. Using a slotted spoon, transfer the tortellini to 4 plates. Divide the chicken and roasted lemon slices among the plates and top with the pan juices. Sprinkle with the remaining 2 1/2 teaspoons tarragon.